Are you planning to screw a light pipe like fiber optic rod on it? You could probably go to the hardware store and get a few cheap screws to verify the thread size.
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Turns out the most common replacement beads are in 6-48, 3-46, or (les common) 5-40 threads.
No local hardware stores carry screws that small.
I went to Sportsman's Warehouse and bought a "Hi-Viz" shot gun light pipe, with a variety of screws. I now know that Rossi used 5-49 screws, and have a highly untraditional yellow fiber front sight on there. I'll replace it with a brass bead, eventually, which may be just as visible, and probably more durable, but for now it will serve fine for repelling boarders.
The good doctor may be along to correct me, but my thought is that what happens inside the target is of primary concern. Even at 5 yards, where the pellets start by making a slug-sized hole, they spread out and make lots of little ones pretty quickly. I'm not sure it matters whether the individual wound paths start close together or with some separation, but I'm pretty sure I like keeping the pellets all headed as close to POA as possible.
https://www.youtube.com/watch?v=JNb2uvezzx0
My better half is on the tiny side, and although she can bust a few clays with a pump 12 gauge, I am looking forward to get her to the range to try out the Ruger PCC I just picked up. Much less recoil and a lot more capacity. Plus plenty of rail space to add a light and red dot. Seems like a great defensive long gun for her (in theory anyways).